feat(escalations): mount time-to-first-action stat-card on /escalations

Surfaces the new GET /analytics/flowpilot/escalations endpoint as a card
above the EscalationQueue list. Closes the loop from yesterday's metric
endpoint commit — seniors and owners see the wedge stat the moment they
open the queue, which is the daily-reps version of the GTM ROI story.

Pieces:
- EscalationMetrics TS interface mirroring the backend Pydantic model
  (incl. metric_definition disclaimer field)
- flowpilotAnalyticsApi.getEscalationMetrics(period) client method
- EscalationMetricCard component:
    * loading skeleton, error state, zero-data empty state
    * avg + median + n_with_action/n_claimed conversion rate
    * humanized seconds → "Ns" / "N.N min" formatting
    * inline disclaimer reminding callers this is in-product time-to-
      first-action only, NOT the savings claim — pair with manual
      baseline (per /codex review's two-metric correction)
- Wired into EscalationQueuePage above EscalationQueue

DS-aligned: card-flat, accent-dim usage held to interactive elements,
text-muted-foreground for secondary copy, font-heading on the headline
number, explicit transition properties (no `transition: all`). Respects
prefers-reduced-motion implicitly (only animation is the loading pulse,
which Tailwind's animate-pulse already gates).

tsc -b clean. No new tests in this commit — component is a thin
state-machine over an axios call; integration coverage comes from the
existing backend tests + the e2e Playwright work in the plan.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/pages/EscalationQueuePage.tsx

@@ -1,6 +1,6 @@
 import { useState } from 'react'
 import { AlertTriangle } from 'lucide-react'
-import { EscalationQueue } from '@/components/flowpilot'
+import { EscalationQueue, EscalationMetricCard } from '@/components/flowpilot'
 
 export default function EscalationQueuePage() {
   const [count, setCount] = useState<number | null>(null)
@@ -21,6 +21,8 @@ export default function EscalationQueuePage() {
         </div>
       </div>
 
+      <EscalationMetricCard period="30d" />
+
       <EscalationQueue onCountChange={setCount} />
     </div>
   )